A liquid crystal display (LCD) is a display device that controls transmission/blocking of light (ON/OFF of display) by controlling the alignment of liquid crystal molecules having birefringence. LCDs employ display modes such as a twisted nematic (TN) mode in which liquid crystal molecules having positive dielectric anisotropy are twist-aligned in the thickness direction of the liquid crystal layer; a vertical alignment (VA) mode in which liquid crystal molecules having negative dielectric anisotropy are aligned vertically to the substrate surfaces; and an in-plane switching (IPS) mode in which liquid crystal molecules having positive dielectric anisotropy are aligned horizontally to the substrate surfaces, and a lateral electric field is applied to the liquid crystal layer.
Since LCDs are thin, light, and consume little power; they are widely used as a display for televisions, personal computers, and PDAs, for example. Particularly in recent years, upsizing of liquid crystal display devices has been rapidly progressing, as represented by liquid crystal display devices for televisions, for example. A suitable mode for an upsized liquid crystal display device is a multi-domain vertical alignment (MVA) mode which provides a wide viewing angle and allows production of a display device in high yield even if the device has a large area. The multi-domain vertical alignment mode vertically aligns liquid crystals having negative dielectric anisotropy, and employs banks (linear protrusions) or notches (slits) in electrodes as structures for alignment control on a substrate. In the MVA mode, such structures for alignment control enable control of the alignment direction of liquid crystals in multiple directions under application of a voltage even if alignment films have not undergone a rubbing treatment. Thus, the MVA mode has a wider viewing angle than the conventional TN mode.
However, the MVA mode has a problem that the display is dark. The main cause is that areas with linear protrusions (ribs) or slits form the boundaries of alignment divisions to generate dark lines which reduce the transmittance during white display, resulting in a dark display. This problem is solved when the distances between the ribs are sufficiently large, but in this case, the number of the ribs which are alignment-controlling structures is reduced. As a result, a longer time is required for alignment stabilization of the liquid crystals upon application of a predetermined voltage, which decreases the response speed. Patent Literatures 1 to 5, for example, teach a technology for providing pretilt angles by use of polymers (hereinafter, the polymers are also referred to as polymer sustained alignment (PSA) layers) which solves the above problems and achieves high luminance and high-speed response.
In the PSA technology, a liquid crystal composition obtained by mixing liquid crystals with polymerizable components such as monomers and oligomers is placed between substrates. Then, the components such as monomers are polymerized into a polymer while a voltage is applied between the substrates to tilt the liquid crystal molecules. Thereby, the liquid crystals are tilted at a predetermined pretilt angle even after elimination of the voltage, so that the liquid crystal alignment direction can be established. Here, the components such as monomers are polymerized by irradiation with heat or light (ultraviolet light). The PSA technology eliminates the need for ribs and thus improves the aperture ratio, and also imparts a pretilt angle smaller than 90° over the entire display region, enabling high-speed response.
For the alignment control of liquid crystals, there is a known method of forming a polymer wall between a pair of substrates of a liquid crystal display device (for example, Patent Literature 6). The polymer wall in the method is a structure formed to surround a liquid crystal layer, and is substantially different from a PSA layer which is a thin layer formed on an alignment film.